Devices for providing positive end-expiratory pressure (PEEP) have been successfully used in the treatment of medical patients having respiratory disorders, such as adult respiratory distress syndrome. The PEEP is provided by restricting the flow of gases exhaled by the patient so that such gases must be exhaled against resistance. In this way the gases exhaled by the patient are subjected to positive pressure resisting exhalation which in turn pressurizes the patient's lungs.
The pressurization of a patient's lungs has been found to be beneficial in treating some respiratory and cardiovascular disorders. It has been found that the provision of PEEP for a medical patient may lower his blood pressure. However, the administering of PEEP interoperatively has not been generally practicable, particularly with the Baincircuit which is described fully hereinafter, due to its interference with anesthesia machines utilized in surgical procedures.
Attempts have been made to provide PEEP for patients being anesthetized but the devices used for providing such PEEP have been found to be awkward. One such device is disclosed in the Wu and Turndorf article found on pages 677 and 678 of Anesthesiology V 43, No. 6, Dec. 1975.
The Turndorf device comprises a conduit through which the patient exhales. A distal end of the conduit terminates in a substantially vertically disposed outlet which is covered by a substantially horizontally disposed valve leaflet. The valve leaflet completely closes off the outlet but is easily pushed out of seating engagement therewith by the gases exhaled by the patient. The requisite flow restriction for PEEP devices is provided by a biasing means which tends to seat the leaflet against the outlet. In the Turndorf device the biasing means comprises a vertically disposed water filled column having a flexible membrane bottom which abuts against the valve leaflet. With this device the gases exhaled by the patient must be of sufficient pressure to overcome the weight of the water in the column biasing the leaflet closed in order to unseat the leaflet and let the gases escape through the outlet.
However, the Turndorf device is prone to leakage and rupture of the flexible membrane bottom. Although such leakage or the like constitutes no threat to the patient, it does result in failure to provide the PEEP effect.
Other attempts have been made to provide PEEP in anesthesia circuits, such as those described by Weeks and Comer in their article beginning at page 578 of Anesthesia and Analgesia Vol. 56, No. 4, July-Aug., 1977. Weeks and Comer endeavored to adapt the Boehringer Laboratories PEEP valve for use with commonly used anesthesia machines. The Boehringer valve is a unidirectional or check valve of the ball type. This valve utilizes a weighted ball which normally blocks flow through the valve when the valve is properly positioned in vertical alignment. In this position the effect of gravity against the ball provides the necessary biasing means for PEEP. However, although this valve is not prone to failure, unless it is malpositioned, it subjects the anesthesia machine with which it is used to backpressure. This backpressure must be compensated for by modifying the anesthesia machine. Such need for modification of anesthesia machines also prevents the general applicablility of PEEP for interoperative procedures.
A further drawback in providing PEEP interoperatively is that no adaptation has been made for providing PEEP in conjunction with the extensively used Bain breathing system or circuit.
The Bain breathing circuit, disclosed in U.S. Pat. No. 3,856,051 and in his article of July 1972 in Canadian Anesthetists Society Journal beginning at page 426, comprises an extension conduit disposed between a reservoir bag of an anesthesia machine and a mask angle. This conduit, which was initially used as a modification for the Mapleson rebreathing system, is used to remove the reservoir bag, a pop-off valve and the like from the immediate vicinity of surgical procedures. This allows the placing of the reservoir bag in a location where it will not be obtrusive during the surgical procedure.
The extension conduit of the Bain circuit is a single limb circuit which conducts gases inhaled and exhaled by the patient to and from the patient and the respirator machine or apparatus. Co-extending longitudinally within the extension conduit is a fresh gas conduit which supplies anesthetic gas to the mask angle from the anesthesia machine.
Dur to the many advantages provided by the Bain circuit it has been widely accepted and is now in general use for surgical procedures. However, since the Bain circuit comprises a single limb for conducting inhaled and exhaled gases, positive end-expiratory pressures devices have not been utilized therewith due to their unidirection flow characteristics. Simply stated, if a unidirectional valve, which provides PEEP, were disposed within the Bain circuit, it would block the flow of gases from the respirator to the patient. Therefore, there has not existed until the present invention a means for providing PEEP in conjunction with this prevalently utilized anesthetic circuit.